Ammonium nitrate propellant composition containing nitrilotriacetate



United States Patent 3,153,604 AWIGNTUM NETRATE PRQPELLANT CQMPOST- TIQNCONTAHNING NETRHLOTRTACETATE Wayne A. Procli, Chicago, and Edwin F.Morello, Juliet, lit, and Gavin H. Peters and Walter W. Butcher,Hammond, Ind, assignors to Standard Gil Company, Chicago, Eli acorporation of Indiana No Drawing. Filed Feb. 23, 1962, Ser. No. 175,3545 Claims. (Cl. 14919) This invention relates to ammonium nitratecompositions suitable for use as gas generating materials andparticularly having propellant utility. More particularly the inventionrelates to an ammonium nitrate propellant characterized by substantialindependence of the burning rate with combustion chamber pressure.

Ammonium nitrate compositions suitable for use as gas generatingmaterials, and particularly the larger shaped configurations used aspropellants are pressure sensitive with respect to the burning rate ofthe composition. Up to this time ammonium nitrate compositions made upof ammonium nitrate, oxidizable organic material, and a combustioncatalyst have exhibited an increase in the burning rate, inches persecond of a strand burning cigarette fashion, with increasing pressurein the combustion chamber. It is difficult to prepare shaped ammoniumnitrate propellants which are absolutely homogeneous and uniform incomposition. These imperfections result in small changes in burning rateand changes in pressure in the combustion chamber. Also in the largerocket motors, it is difiicult to maintain chamber pressure absolutelyconstant over a prolonged burning period. The usual variation in burningrate with pressure variation is sufficient to affect the accuracy of aballistic missile. A composition which showed substantially no burningrate variation over even a narrow pressure range would be of inestimablevalue to rocketry.

An ammonium nitrate composition has been discovered which exhibits noburning rate variation substantially within the error of determinationof such rates over combustion chamber pressure variation range of asmuch as 500-600 p.s.i. This flat burning rate occurs in a pressure rangewhich is of particular usefulness in propulsion applications, namely, inthe region of 1000-1600 p.s.i. combustion chamber pressure.

The solid propellant composition of the invention consists of:

Component About, weight percent Cellulose acetate 7-10 Acetyl triethylcitrate 7-10 Dinitrophenoxyethanol 7-10 Alkali metal aminobenzoate 1-4Finely divided carbon 3-5 Ammonium oxalate 0.5-2 Ammoniumnitrilotriacetate 1-2 Aromatic hydrocarbon amine gassing inhibitor0.5-1.5 Phenylmorpholine 0.5-1 RNH(CH NH where R is alkyl having about8-20 carbon atoms and x is an integer from 2 to 4 0.1-0.5 Nonionicsurfactant 0.0-0.6 Ammonium nitrate Remainder The term ammonium nitrateas used in this specification and in the claims is intended to meaneither C.P. grade or ordinary commercial grade ammonium nitrate ormilitary grade. The particles may be coated with a small amount ofmoisture-resisting material such as petrolatum or paraflin. A minoramount of other inorganic nitrates such as sodium nitrate and/ orpotassium nitrate Patented (Jet. 20, 1964 ice nay be present. Finelyground ammonium nitrate is preerred.

The combustion catalyst utilized in the composition of the invention isan alkali metal salt of aminobenzoic acid. The sodium salt of orthoaminobenzoic is preferred. Hereinafter, the preferred salt is identifiedby the trivial name, sodium anthranilate.

The composition of the invention includes in its content of oxidizableorganic material, as a cooling material, an ammonium oxalate andpreferably diammonium oxalate.

The composition of the invention includes an oxidizable materialfunctioning as a stabilizer. This stabilizer is a salt of a nitrogenbase and nitrilotriacetic acid; preferably the stabilizer is ammoniumnitrilotriacetate.

The composition of the invention also includes phenylmorpholine, whichmay be the pure compound or commercial technical grade material.

Further, the composition includes an N-alkyl substituted polymethylenediamine where the alkyl substituent which has 8-20 carbon atoms, and thenumber of methylene groups are 2-4. This diamine may be represented bythe formula RNH(CH NH Where R is alkyl and has 8-20 carbon atoms and xis an integer from 2-4. It is preferred to utilize the N-alkylsubstituted Lil-propylene diamines where the alkyl substituent contains14-18 carbon atoms. This class of diamines is available commerciallyunder the trade name Duomeen. A particularly suitable material is thatavailable as Duomeen T which has the 1,3-propylene diamine backbone withthe N-alkyl substituent derived from tallow fatty acids.

The composition of the invention includes as a burning rate acceleratorfinely divided carbon. The carbon component of the propellantcomposition includes finely divided, highly adsorptive activatedcarbons. These are well known in the art of decolorizing sugar andadsorption of gases. Examples of these are Norit and Nuchar, the formerbeing a high-adsorptive activated carbon used to absorb odors, and todecolorize water, gases, chemical solutions, oils and greases. Nuchar isan activated carbon made from a residual organic material obtained inthe manufacture of cellulose and is characterized by high porosityresulting in high adsorptive capacity. Like Norit it is used as adecoloring and deodorizing agent. 1

A second general class of carbon useful for increasing the burning rateof the propellant composition are the flames, furnace combustion blacksproduced by the par tial combustion of essentially gaseous hydrocarbonsin closed retorts and furnace thermal blacks produced by thermaldecomposition of hydrocarbons such as acetylene in preheated furnaces.The carbon blacks are characterized by low ash content by havingextremely small particle size, that is, 50 to 5000 A., and containadsorbed hydrogen and oxygen. Other carbon blacks which may be used inthe propellant grains are lamp blacks produced by burning liquid fuelssuch as petroleum oils, tars and aromatic residues in specially designedpans, combustion taking place under restricted air supply conditions.The carbon blacksas indicated above are generally characterized byexceedingly small particle size, that is, well below #325 U.S. Standardsieve particle size. However, to avoid dusting and convenience inhandling, some carbon blacks are formed to the so-called bead typecarbon blacks which beads'are generally of such dimensions as to passthrough a #20 U.S. Standard sieve and are retained on a #200 U.S.Standard sieve. The beads are very soft and are physically unstable'as'beads and become disintegrated to smaller than #325 U.S. Standardsieve 'during the mixing and milling of the composited propellantcomponents as described hereinbelow. The carbon blacks are of low ashcontent, and usually contain less than 0.5% ash. Examples of bead typecarbon blacks are Micronex Beads (channel blacks) and Statex Beads(furnace blacks).

A third type of carbon which is useful for improving the burning rate ofour gas-producing propellant composition is graphite, flake andamorphous. If desired from a natural graphite, the ash content should bereduced below about which can be accomplished by treating the-naturalproduct by air flotation or the ash content may be reduced by leachingwith mineral acid or by other methods well known to the art. We prefergraphite of colloidal or semi-colloidal particle size.

Still another type of carbon which we have found effective forincreasing the burning rate of the gas-forming composition is finelyground petroleum coke, particularly petroleum coke obtained as a residuein the pipe-stilling of Mid-Continent heavy residuums. Such coke usuallycontains less than about 1% ash and is preferably pulverized to passthrough a #325 US. Standard sieve prior to incorporation in thegas-producing propellant composition. The coke may be activated bymethods well known to the art to improve the efficiency thereof as aburning rate promoter in our propellant composition.

Ammonium nitrate compositions in general tend to develop gas in storageat elevated temperatures. The composition of the invention includes agassing inhibitor component. Aromatic amines when introduced into theammonium nitrate based grain containing catalyst and finely dividedcarbon have the very desirable characteristic of decreasing the amountof gassing in high temperature storage and frequently even eliminatingor essentially eliminating gassing for prolonged periods of time. Thearomatic amine gassing inhibitors of this invention are illustrated bydiphenylamine, dinaphthylamine and phenyl naphthylamine. In the case ofthe naphthyl amines, the linkage between the naphthyl radical and thenitrogen may be either alpha or beta. And those amines represented bythe empirical formula In this empirical formula Z is an aromatic nucleusselected from the class consisting of phenyl and naphthyl; R is selectedfrom the class consisting of hydrogen and alkyl containing from 1 to 12carbon atoms; R and R" are selected from the class consisting ofhydrogen, and alkyl containing from 1 to 4 carbon atoms; and x is aninteger from 1 to 3.

Examples of monoamino-containing compounds are: aniline(monophenylamine, monoamino benzene), 1- naphthylamine, toluidine(methyl aniline) xylidine (dimethylaniline), dodecyl aniline, N-methylaniline, N,N- dimethyl aniline, N-sec-butyl aniline.

Examples of the diamino compounds are: diamino benzene (phenylenediamine), diamino toluene (toluene diamino), diamino naphthylene, methyldiamino naphthylene, dodecyl diamino naphthylene, N-sec-butyl, diaminobenzene, N,N'-di-sec-butyl diamino benzene, and N-methyl diaminonaphthylene.

Examples of triamino compounds are: triarnino benzene, triaminonaphthylene, triamino toluene, and triamino methyl naphthylene.

The composition of the invention may include one or more nonionicsurfactants which tend to improve mixing of the composition and moldingof shaped configurations. Any nonionic surfactant which is inert to theother components of the composition is suitable for use in thecomposition. For purposes of illustration, only certain broad classes ofnonionic surfactants are set out hereinafter.

The surfactant polymers of alkylene oxides may be the polymers ofethylene oxide, copolymers of ethylene oxide and propylene oxide orblock polymers of propylene oxide 4% and ethylene oxide wherein ethyleneoxide is added to polymers of propylene oxide. These polyalkylene oxidecondensation products are otherwise known as polyoxyallrylene glycolsand have from two to three carbon atoms in the oxyallrylene unit.

One class of the polyoxyalkylene glycols which are effective are thecommercial Pluronics which are polyoxypropylene-polyoxyethylene glycolsor specifically, block copolymers. Pluronic L-62 has a molecular weightof about 2,000 of which 2,000 molecular weight from about 1500 to about1800 is furnished by the propylene oxide units, the other alkylene oxideunits in the polymer molecule being ethylene oxide units. The generalformula for the Pluronics is Thus b in this formula, for Pluronic L-62,has a value of about 26 to about 31. Pluronic IP62 is a liquid having aviscosity at 25 C. of 300 to 500 centipoises.

As indicated hereinabove, derivatives of the polyoxyalkylene glycols areeffective to reduce the consistency of the ammonium nitrate-binder'mixtures. Certain of these derivatives are the fatty alcohol monoethersand the fatty acid monoesters. An example of the monoether derivative isTergitol XC. Tergitol XC is a monoether derivative of a copolymer ofethylene oxide and propylene oxide and has the approximate formulawherein R is an acyclic hydrocarbon radical containing from 12 to 20carbon atoms. The aklyene oxide constituents of the molecule eachcontribute about 1500 to give about 3000 to the total molecular weight,i.e., not more than about 3300, of the monoether derivative. In theseether derivative-type surfactants the number of ethylene oxide units mayvary from about 22 to 35 and the num ber of propylene oxide units mayvary from about 18 to about 27. The total molecular weight of theseethers will usually lie within the range of from about 2000 to about3300.

An example of a monoester derivative of a polyoxyalkylene glycol whichis effective is the commercial product Nonisol-ZSO. This product is amono-oleyl ester of polyoxyethylene having a molecular weight of about1000. The fatty acid esters of polyoxyethylene sorbitol condensationproducts are effective surfactants for purposes of this invention. Thesemay be produced by condensing ethylene oxide or polyoxyethylene withsorbitol followed by esterification of the condensation product with a12 to 20 carbon atom fatty acid. In general, suitable products of thistype have molecular weights within the range of from about 1000 to about3300.

The term polyoxyalkylene glycol, ether and fatty acid ester derivativesthereof, as used in this specification and claims includes (1) thepolyethylene oxide homopolymers, copolymers or ethylene oxide andpropylene oxide, block copolymers or propylene oxide and ethylene oxide,said polymers having a molecular weight within the range of from about1000 to about 3000, (2) the monoethers of the polymers of (1) producedby reacting fatty alcohols and mercaptans having 10 to 20 carbon atomswith polymers of (1) said ethers having a molecular weight of about 2000to about 3300, and (3) monoesters of the polymers of (1) produced byesterification of said polymers with fatty acids having from 12 to 20carbon atoms per molecule, said monoesters having molecular weightswithin the range of about 1000 to about 3300. The fatty acids used toesterify the condensation product of ethylene oxide with sorbitol havefrom 12 to 20 carbon atoms, and the fatty acid esters produced havemolecular weights within the range of from about 1000 to about 3300.

Particularly effective are the nonionic surfactants which may beclassified as esters of monoanhydro sorbitols described in US.2,398,193. These are known commercially as the Span and Arlaceldescribed on page 3 of a brochure entitled Atlas Surface Active Agents,issued in 1950. The sorbitans are mixtures of cyclized monoanhydrizedsorbitol. The preferred Span materials for use in the composition areessentially partial esters of oleic acid and sorbitol monoanhydrides(sorbitans) derived from sorbitol, the sorbitan oleates being mixturescontaining an average of from 1 to 3 oleyl radicals for each molecule ofanhydrized sorbitol. Sorbitol is dehydrated to give condensed linkstructures or sorbitans which, when esterified with oleic acid, producethe preferred Spans or Arlacels. Arlacel C, which is sorbitansesquioleate, has been found to be particularly effective as an additiveto promote ballistic dependability of the grain compositions. Thismaterial is an oily liquid at 25 C. having a specific gravity of0.95-1.00, a flash point of about 450 F. and a fire point of about 530F.

Arlacel C has a viscosity at 25 C. of 9001100 centipoises. Another veryeffective nonionic surfactant is Span 85, which is a sorbitan trioleatehaving a viscosity at 25 C. of 100-250 centipoises. It has a specificgravity of 0.92-0.98, a fiash point of 500 F. and a fire point of 570 F.

With the exception of the hereinabove defined combusion catalyst and theammonium nitrate, the other components of the composition may beconsidered as oxidizable organic materials. In a narrower sense, organicmaterials are present to function as a binder for the ammonium nitratecatalyst and other solid components. The binder material utilized in theinstant composition consists of cellulose acetate, acetyl triethylcitrate and dinitrophenoxyethanol.

The acetyl triethyl citrate is a well known plasticizer. The citrate maybe the pure compound or commercial technical grade.

The dinitrophenoxyethanol component may be essen tially pure material,or more usually will be a mixture of one or more of thedinitrophenoxyethanols and a bis- (dinitrophenoxy)ethane. In all cases,the dinitrophenoxyethanol is the predominent member and usually willrepresent 70% or more of this component. A mixture of2,4-dinitrophenoxyethanol and l,2-bis-(2,4-dinitrophenoxy)ethane isparticularly suitable. US. Patent No. 2,935,415 at columns 2 and 3 setsout a description of classic methods of preparation of the mixture ofthe two materials and the separation thereof. US. Patent No. 2,988,571sets out a method of preparation of high purity dinitrophenoxyethanol.

The polymeric material present in the binder is cellulose acetate.Particularly suitable are the cellulose acetates which have combinedacetic acid contents on the order of 5058%. A preferred celluloseacetate is one made by the Celanese Company as grade HLFS-93, which hasa combined acetic acid content of about 55%.

Examples Two illustrative examples of the results obtainable in terms ofuniformity of burning rate with Variation of pressure are set out. Theburning rate-pressure results set out below were obtained by burning astrand at a given pressure in the well known Crawford bomb test whereina strand of a definite shape is burned at a given temperature andpressure, and the burning rate, cigarette fashion, is obtained. In thesetests two batches of propellant composition containing the identicalpercentage of each component were prepared. Each batch repre sentedapproximately 20 quarts US. of propellant composition. While thecomponent percentages were identical, the conditions of blending werevaried between the two batches in order to observe whether or not theco1nposition would give a flat burning rate plateau of its burningrate-pressure curve regardless of the method of blending utilized. It iswell known that the burning rate of a propellant composition can bechanged by the degree of mixing or the type of mixing used in thepreparation of the composition. This' composition follows this samepattern as is shown in the burning rate data below; The data doestablish that the degree of mixing has no bearing on the flat burningrate characteristic of the composition.

In general, the blending operation utilized in the preparation of thetwo batches of propellant utilized in the burning rate tests followsthat of the prior art, such as described in US. Patent No. 2,987,388 ofWilliam G. Stanley, assigned to Standard Oil Company (Indiana).

The propellant utilized in these tests contained the followingmaterials.

Component: Percent by weight Cellulose acetate (cellulose HLFS-93) 8.91Acetyl triethyl citrate 8.91 Dinitrophenoxyethanol 8.12 Sodiumanthranilate 2.00 Carbon black 4.00 Ammonium oxalate 1;0O Ammoniumnitrilotriacetate 0.90 Toluene diamine 0.50 Phenylrnorpholine 0.50Duomeen T 0.10 Arlacel C (sorbitan sesquioleate) 0.10 Nonic 259(polyethylene glycol tertdodecyl thioether) 0.03 Ammonium nitrate(Spencer C.P.) 64.93

The burning rate data obtained for the two batches are set out below.

Pressure (p.s.i.) Batch 1 Batch 2 9099999999 Ooooqqq 9999999999UJQNQOBGBOBO'JQOI NGrPOsOQOWWNQ The above data establish that batch No.1 shows essentially no variation in burning rate beyond the error ofdetermination of these rates over the region 1000 1600 p.s.i. Batch No.2 shows essentially no variation in burning rate over the range of1000-1500 p.s.i. It is considered that the difference in burning rate atthe standard pressure of 1000 p.s.i. is normal for the difference inmixing technique-herein the severity of the blending operation-known toexist between the two batches of propellant.

Thus having described the invention, what is claimed is:

1. A solid composition consisting of cellulose acetate, about 740%;acetyl triethyl citrate, about 7-10%; dinitrophenoxyethanol, about7-10%; alkali metal aminobenzoate, about 14%; finely divided carbon,about 3- 5%; ammonium oxalate, about 0.52%; ammonium nitrilotriacetate,,about 12%; aromatic hydrocarbon amine gassing inhibitor, about 0.5-1.5%;phenylmorpholine, about 0.51%; a diamine of the formula are selectedfrom the group consisting of hydrogen, and

alkyl containing from 1 to 4 carbon atoms; and x is an integer from 1 to3.

2. The composition of claim 1 wherein said gassing inhibitor is toluenediamine.

3. The composition of claim 1 wherein said diamine is an N-alkylpropylene diamine Where the alkyl substitucnt is derived from saturatedtalloW fatty acids.

4. The compositions of claim 1 wherein said surfactant is sorbitansesquioleate.

5. A solid composition consisting of cellulose acetate, about 9%; acetyltriethyl citrate, about 9%; dinitrophenoxyethanol, about 8%; sodiumanthranilate, about 2%; carbon black, about 4%; diammonium oxalate,about 1.0%; ammonium nitrilotriacetate, about 1%; toluene diaminegassing inhibitor, about 0.5%; phenylmorpholine, about 0.5%; a diamineof the formula RNI-I(CH NH Where R is alkyl having 1418 carbon atoms andx is 3, about 0.1%; sorbitan sesquioleate, about 0.1%; polyethyleneglycol tertdodecyl thioether, about 0.03%; and the remainder of saidcomposition being ammonium nitrate.

References Cited in the file of this patent UNITED STATES PATENTS 102,938,778 Linsk May 31, 1960 2,942,964 Burgwald et al June 28, 19602,946,671 Marti July 26, 1960 2,973,255 Eiszner Feb. 28, 1961

1. A SOLID COMPOSITION CONSISTING OF CELLULOSE ACETATE, ABOUT 7-10%;ACETYL TRIETHYL CITRATE, ABOUT 7-10%; DINITROPHENOXYETHANOL, ABOUT7-10%; ALKALI METAL AMINOBENZOATE, ABOUT 1-4%; FINELY DIVIED CARBON,ABOUT 35%; AMMONIUM OXALATE, ABOUT 0.5-2%; AMMONIUM NITROLOTRIACETATE,ABOUT 1-2%; AROMATIC HYDROCARBON AMINE GASSING INHIBITOR, ABOUT0.5-1.5%; PHENYLMORPHOLINE, ABOUT 0.5-1%; A DIAMINE OF THE FORMULA